Oxidation resistant bimetal



OXIDTION RESISTANT BIMEIL Fild July 17, 1951 WITNESSESI Patented Oct. 10, 1933 UNITED A STATES 1,929,655 OXIDATION RESISTANT BIMETAL AHoward Scott, Wilkinsburg, Pa., assignol to Westinghouse Electric & Manufacturing Company,

a corporation of Pennsylvania Application July 17, 1931. Serial No. 551,441 3 Claims. (CL 297-15) .My invention relates to thermally actuable lde-y vices and particularly to bimetal thermostatic elements. An object oi my invention 5 metal. element that shall be made of material capable of resisting oxidation, able to withstand subjection to relatively high temperatures, be able to withstand repeated cycles of heating and cooling without loss of strength and have a linear deflection in accordance with temperature changes. In practicing my invention, I provide a bimetal element, both components of which include an appreciable, but not major, percentage of chromium, relatively small percentages each of silicon, manganese and carbon, the remainder being iron. The high-expansion component has not over 9% of chromium and need not contain over 25% of nickel, although a vhigher nickel content is permissible, while the low-expansion component may have a chromium content varying '8% to 23% and traces only of nickel. 1

The single iigure of the drawing is a view, in section, of a bimetal bar embodying my invention.

Referring to the drawing, I have indicated a bimetal bar as including a high-expansion component 11 and a low-expansion component 12, each of a composition to be hereinafter set forth, the two components or elements being suitably secured together, as by. welding, in a manner now well known in the art. While I have indicated a specific form of bimetal element, such as a bar, my invention is not limited theretov but resides more particularly in the compositions of the two components of the device.

One of. the relatively dilcult a bimetal thermostat is that of beingutilized to signal or indicate the failure of a pilot name, and, in an application of this kind, it is n ecis to provide a bi' is free to move in response to temperature varia-` tions, shall be linear, that is, it shall be the same applications of per unit change of temperature at any part oi its working range of temperature.

I have found that such characteristics are inherent in a bimetal element including two chromium steels, one of which contains sufilcient nickel, together with manganese and carbon, to render it substantially non-magnetic at atmospheric temperatures. This non-magnetic alloy has a high expansivity, nearly that of brass. My other chromium steel contains little or no nickel,

and is magnetic. Usually, it contains a larger percentage of chromium than the non-magnetic mainder being iron and traces of other elements which may be considered impurities. By nickel, I mean to include commercial nickel, which usually has a small quantity of cobalt mixed in with it. e.

The low-expansion component 12 may have a chromium content varying between 8% and 23%, or possibly more, a nickel content so small that it may be considered an impurity, that is, below 1%, a silicon content of the order of .1% to 3% or even more, a manganese content of the, order of .2% to 1%, a carbon content less than .5%, the remainder being iron and traces of other 40 essary that the bimetal element shall have a elements. These proportions for the two elerelatively high' resistance to oxidation. A furments 11 and 12 are preferred values, and are ther very desirable characteristic is that the given mainly to indicate certain alloys which bimetal element shall have suiiicient mechanical are possible to be used,

45 strength to be able to withstand subjection t0 A. suitabIe bimetal nementV may be chosen temperatures of 5001C. or over without loss of from'the following compositions: mechanical strength, even after having been subf v jected to a relatively large number of cycles of f heating and cooling; That is, it is higmy de- Cmpm 50 sirable that the deection be always the same A1105' WW l for a given temperature variation, in order to %Cr %Ni %si %M %o avoid recalibration or resetting of the adjustable"element of the device. A relatively large ggg g-g 344; deiiection is not of as great importance in an ap- A 1310 012 da 011s'j ol 1 55 plication of this kind as are the other character- 3:? gigi gistics hereinbefore set forth. Another desirable characteristic is that the deflection of a bimetal y bar, when one of its ends is fixed and the other 'The alloys identified by I and l1 are highexpansion steels and those identiied by A, B and C are comparatively low-expansion steels.

-bar, sheet or disc.

of mechanical stre Their expansion is given approximately in the following'table:

portional to the difference in expansivity of the components. From the difference between the best tabulated values it is apparent that the deflection of such a bimetal element is nearly as high as that of monel and 42 percent nickel steel and that it is practically linear.

I have found that it is relatively easy to fabricate my bimetal elements by suitably welding together relatively heavy ingots of the two alloys at a relativehr high temperature and then rolling the same to thedesired thickness of the bimetal Samples of such bimetal elements have withstood the oxidizing eifect of high temperatures-on the order of 500 C. and

over, and the deflection is a linear one, that is, it variesin accordance with the variation of the temperature, fand I have found that the deflection per unit change of temperature is substantially the same over a temperature range of 100 C. andl500 C. Y y

The bimetal element embodying my invention thus provides a thermally actuable metallic thermometer structure which is highly resistant to oxidation, which will stand subjection to a large number of cycles of operation without loss h, which will standrelatively high temperat es without loss of mechanical strength, and the deflection of which is substantially a linear function of temperature change.

As various modifications may be made in the device embodying my invention without departving from the spirit and vscope thereof, I desire that only such limitations shall be placed thereon as are imposed'by the prior art.

.tween .61% and .82% manganeserapproximately I claim as my invention: y

1.,A bimetal element having a high-expansion component of the following composition; approximately 5.7% chromium, approximately 22% nickel, approximately .2% silicon, approximately seven-tenths per cent of manganese, approximately forty-seven hundredths per cent of carbon and substantially all of the remainder iron, and having a low-expansion component of the following composition; approximately 17% chromium, approximately one per cent each of silicon and manganese, from one-tenth per cent to forty-live hundredths per cent of carbon, a trace of nickel and substantially all of the remainder iron.

2. A bimetal element including two chrofmium-steel alloys of different temperatures expansivities, the high-expansion component having the following composition: -P

` el.' tent Chromium 2. to 9. Nickel 18. to 25. Silicon .1 to 2. Manganese --2 .4 to 2. Carbon approximately .47 1.00 Iron reminder and the low-expansion component'having the following composition: Y

. Per cent Chromium 8. to 23. Nickel traces Silicon I .1 to 3.2 Manganesem .2 to 1. Carbon .1 to .45

.non remainder 110 3. A bimetal element having 'a high expansion component of the following composition; .between 7.2% and 7.8% chromium. between 19.5% and 21.9% nickel, between .78% and 1.87% silicon. be-

.47% carbon, the remainder being principally iron, and a low expansion component of the following composition; between 8.4% and y 20.3% chromium, between .3% and`3.2% silicombetween .1% and .6% nickel, between .5% and .85% manganese, between.1% and .45% carbon, the remainder being principally iron.

j HOWARD Sco'rr. 125 

